Bleach activators are compounds that react in aqueous solutions containing hydrogen peroxide or perhydrates, with the formation of peracids that have a bleaching effect. Especially active bleach activators include N-acylated amines, amides, glycolurils that are known from, for example, U.S. Pat. Nos. 3,163,606, 3,177,148, 3,775,332, 3,812,247, and 3,715,184, all of which are incorporated herein by reference. In U.S. Pat. No. 3,163,606, there is a suggestion that these bleach activators should be provided with a water-soluble coating, which coating may consist of carboxymethyl cellulose, for example, prior to their further application, particularly before use in washing agents and bleaches. This coating agent may be sprayed on the activator in finely powdered form dissolved in water, after which the coated material is dried. It is recommended that the activator be granulated before coating, but there are no indications given as to the method and granulating adjuvants to be used.
When the procedures disclosed in U.S. Pat. No. 3,163,606 are implemented, considerable problems are encountered when a bleach activator such as, for example, tetraacetylethylenediamine, is sprayed with an aqueous carboxymethyl cellulose solution in a granulator. This is so because aqueous solutions with a content of more than 5 percent by weight of carboxymethyl cellulose no longer can be worked in technical granulating processes due to their high viscosity and gel-like consistency. Consequently, very large amounts of the relatively very dilute cellulose ether solutions must be used to produce a sufficiently strong coating layer on the activator particles.
When an amount of 18 percent by weight of carboxymethyl cellulose is to be applied to the bleach activator, as stated in Example 10 of U.S. Pat. No. 3,163,606, and when it is assumed that a 5 percent solution is used that still is workable with respect to its high viscosity, then 360 percent by weight (based on the amount of activator) of a 5 percent cellulose ether solution would be required for this purpose. However, it can be demonstrated that lumpy to pulpy masses instead of suitable granulates are formed when more than 20 to 30 percent by weight of such a solution is used. This is the reason for the recommendation in Column 3 of U.S. Pat. No. 3,163,606 that alcoholic solutions of carboxymethyl cellulose be used. Unfortunately, the use of such solutions necessitates the installation of expensive protection against explosions and leads to high costs for the recovery of the solvent, and such a procedure is unsuitable for commercial purposes. The same problems are encountered when the cellulose ether solution is replaced by the fatty acids, fatty acid alkanolamides, fatty alcohols, or Carbowaxes also suggested in U.S. Pat. No. 3,163,606, dissolved in organic solvents, as coating material. An added complication is that such coating materials dissolve either not at all or only very slowly in cold bleach solutions and the desired cold-bleaching effect thus is suppressed.
U.S. Pat. No. 3,789,002 discloses a process for the preparation of coated, granulated bleach activators in which the activator first is mixed dry with a substance suitable for coating or granulation and, in a second step, is then sprayed and granulated with water or granulating adjuvants dissolved in water or film-forming agents. The substances proposed for the preparation of the dry premixes are either water-soluble builder salts normally used in washing agents, such as phosphates, polyphosphates, carbonates, and silicates of alkali metals that bind water of crystallization, or fillers that are insoluble in water, such as silicic acid, magnesium silicate, or magnesium oxide. The same water-soluble salts that bind water of crystallization also may be used as granulating adjuvants, or the dry premixes may be sprayed with an aqueous solution of film-forming substances such as cellulose derivatives, or of other water-soluble polymers of natural or synthetic origin, and granulated simultaneously. However, this method is suitable only for the preparation of granulates with a relatively low content of bleach activators, i.e. with one of less than 50 percent by weight. Consequently, the granulates can be used only in those areas where the high content of additives does not interfere.
Thus, there has been a need to develop a process for the preparation of free-flowing, uniformly coated, and consequently very stable bleach activator granulates that have a considerably high content of active substance, for example, 90 percent by weight and more.